A. Field of the Invention
The present invention relates generally to techniques for measuring characteristics of systems. More particularly, this invention relates to the measurement of the reflection coefficients in stored energy systems.
B. Description of the Related Art
Reflection coefficients have been conventionally calculated by suppressing a forward wave that is incident on a device or transmission line under test (DUT or LUT), measuring a wave reflected from the DUT or LUT, and calculating the ratio of the reflected wave to the forward wave. Alternatively, the reflection coefficients have been calculated by measuring a standing wave produced by the combination of forward and reflected waves.
The forward wave may be suppressed by a directional coupler or a directional bridge. The use of a coupler or bridge presents difficulties for wideband measurements. For example, the balance in bridges depends on how well the impedance of the DUT or LUT matches the impedance of the bridge. A good match is hard to achieve between conventional twisted-pair lines associated with the DUT and a bridge.
Impedance matching is also a problem associated with the use of directional couplers. Specifically, it is difficult to achieve good impedance matches both at the interface between the directional coupler and the measurement device, and at the interface between the directional coupler and the DUT or LUT. Furthermore, even in systems that are well matched, when the signal reflected from the DUT or LUT has a low magnitude it becomes extremely difficult to calculate the reflection coefficient by measuring the composite signal (i.e., the reflected signal and the forward signal). Therefore, there is a need in the art for a reflection coefficient measurement system that allows the conventional suppression of a forward wave while also suppressing the reflections that occur as a result of the mismatch at the interface between the DUT or LUT and the instrument used for suppressing the forward wave. Further, there is a need in the art for increasing the dynamic range of the measurement system by enabling the efficient calculation of reflection coefficients when the reflected wave has a low voltage level.
Accordingly, it is an objective of the present invention to meet the foregoing needs by providing systems and methods for measuring reflection coefficients.
Methods and systems consistent with the present invention measure reflection coefficients by exciting a device under test with a driving signal and measuring the driving signal incident on the device under test. After the driving signal level is measured, the source providing the driving signal is removed. A signal reflected from the device under test is sampled at a sample time that may differ from the frequency of the driving signal. Finally, the reflection coefficient of the device under test is calculated by dividing the measured level of the reflected signal by the measured level of the driving signal.
Both the foregoing general description and the following detailed description provide examples and explanations only. They do not restrict the claimed invention.